The present invention relates to a process for the fixed bed sweetening of petroleum distillates using halogenated metal phthalocyanine as a catalyst.
Particularly the invention relates to the development of a process for fixed bed sweetening of petroleum fractions like FCC gasoline, jet fuel, kerosene, ATF, heavy naphtha thermal gasoline, diesel and distillate fuel oil using halogenated metal phthalocyanine as catalyst.
It is well known that the presence of mercaptans in the petroleum products like LPG, naphtha, gasoline, kerosene, ATF etc. is highly undesirable due to their foul odour and highly corrosive nature. These are also poison for the catalysts and adversely affect the response of TEL (tetraethyl lead) as octane booster. Although there are several processes known for the removal of mercaptans from these petroleum products, the most common practice is to oxidize the mercaptans present to less deleterious disulphides with air in the presence of a catalyst. Commonly lower mercaptans present in LPG, pentanes, LSRN are first extracted in alkali solution and then oxidized with air in the presence of a catalyst. The higher molecular weight mercaptans present in petroleum products like FCC gasoline, natural gas liquid (NGL), LSRN, thermal gasoline and distillate fuel oil are oxidized to disulphides with air in presence of alkali in a fixed bed reactor containing catalyst impregnated on a suitable support (Catal Rev. Sci. Eng. 35(4),571-609(1993).
In the hitherto known processes, phthalocyanines containing metals like cobalt, iron, manganese, molybdenum and vanadium are used to catalyze the oxidation of mercaptans to disulphides in alkaline medium. Among these cobalt and vanadium (especially cobalt) phthalocyanine and their derivatives are preferred. As these metal phthalocyanines are not soluble in aqueous medium, for improved catalyst activity their derivatives like sulphonated and carboxylated metal phthalocyanines are used as catalysts for sweetening of petroleum fractions. Various catalysts reported are cobalt phthalocyanine monosulphonate (U.S. Pat. Nos. 3,371,031; 4,009,120; 4,207,173; 4,028,269; 4,087,378; 4,141,819; 4,121,998; 4,124,494; 4,124,531), cobalt phthalocyanine disulphonate (U.S. Pat. No.4, 250,022), tetrasulphonate (U.S. Pat. No. 2,622,763), mixture of mono- and disulphonate (U.S. Pat. No. 4,248,694), phenoxy-substituted cobalt phthalocynine (Ger. Offen 3,816,952), cobalt and vanadium chelates of 2,9,16,23-tetrakis (3,4-dicarboxybenzoyl) phthalocyanine for both homogeneous and fixed bed mercaptan oxidation (Ger. offen 2,757,476: Fr. Demande 2,375,201) and cobalt and vanadium chelates of tetrapyridinoporphyrazine (Ger. offen 2,441,648).
It is also hitherto known that because of poor solubility of cobalt phthalocyanine in aqueous or other medium it is difficult to impregnate the same on the bed of catalyst support material. The highly sulphonated or other similar derivatives of cobalt phthalocyanine, though are soluble in the impregnating solution, their high solubility makes it difficult to place the required amount of catalyst on the support material. Furthermore, the more highly sulphonated or other similar substituted metal phthalocyanines are susceptible to leaching from the catalyst support when it is made alkaline with sodium or potassium hyroxide solution. The leaching causes loss of catalyst from the bed.
Metal phthalocyanine monosulphonate are thus the preferred compounds for impregnation on the support material in the fixed bed sweetening. The most common method used for their preparation is the reaction of metal phthalocyanine with oleum or sulphuric acid. However this reaction is difficult to control so as to produce metal phthalocyanine monosulfonate, exclusively because in this reaction, along with monosulphonate di- and tri- sulphonated derivatives are also formed. These derivatives of metal phthalocyanines, especially of cobalt phthalocyanine are much more soluble in hydrocarbon and in caustic solution than the former. This solubility characteristic is very important when the catalyst is used for the fixed bed sweetening of petroleum fractions. The catalyst once placed on the carrier must remain attached so that catalytic activity is maintained. The catalyst therefore should be such that it could be easily impregnated on the fixed bed material and yet is not leached out by alkali solution or hydrocarbons during the sweetening process.
The main objective of the present invention is to provide a fixed bed process for the sweetening of petroleum fractions like kerosene, ATF, FCC gasoline, heavy naphtha, thermal gasoline; diesel and distillate fuel oil using halogenated metal phthalocyanine, as catalyst impregnated on a suitable support.
In another objective of the present invention the halogenated metal phthalocyanine could be dichloro or dibromo; diodo-, monochloro., mono-bromo; monoiodo- or similar derivatives of metal phthalocyanimies, preferably dichloro- or dibromo- derivatives of cobalt and iron phthalocyanine. These halogenated metal phthalocyanines can be prepared by treating the metal phthalocyanine with any conventional halogenating agent like chlorine, bromine, iodine, thionyl chloride, sulphuryl chloride, phosphorus pentachloride, phosphorus oxychloride, phosphorus pentabromide, phosphorus trichloride or similar halogenating agent, without any solvent or in solvents like dichloro benzene, nitrobenzene.
In another objective of the present invention provides a method for the impregnation of these novel sweetening catalysts on a suitable support material with catalyst dispersion on the support by circulating alcoholic alkaline solution of the catalyst through the bed till colourless solution is obtained in the effluent. The support material can also be impregnated by dipping, soaking, suspending or otherwise immersing the support in the form of spheres, pills, pellets, granules or other particles of uniform or irregular shape in alcoholic alkaline solution of the catalyst. The loading of the catalyst on the support material may vary from 0.01-5% preferably 0.1-1%. For making alcoholic alkaline solution, alcohol like methanol, ethanol etc. and alkalis like sodium hydroxide, potassium hydroxide or any other alkali may be used. The suitable support material includes naturally occurring clays and silicates for example diatomaceous earth, fuller""s earth, Kieselguhr, feldspar, montmorillonite, hallogsite, Kaoline and the like; various charcoals produced by destructive distillation of wood, peat, lignite, nutshells, bones and other carbonaceous matter; naturally occurring or synthetically prepared inorganic oxides such as alumina, silica, zirconia, thoria, boria etc. or combinations thereof like silica-alumina, sillca-zirconia, alumina-zirconia etc. The preferred support material being charcoals with highly porous particle structure of increased adsorbent capacity generally defined as activated charcoal.
Accordingly the present invention provides a process for the fixed bed sweetening of petroleum distillates using halogenated metal phthalocyanine as a catalyst which comprise; impregnating the catalyst on activated charcoal bed by circulating alcoholic alkaline solution of the catalyst through charcoal bed till colourless solution is obtained in the effluent, passing the petroleum distillate through above said catalyst loaded charcoal bed along with air or oxygen at a temperature in the range of 20xc2x0 C. to 100xc2x0 C. and at a pressure in the range of 1kg/cm2 to 15 kg/cm2 with a liquid hourly space velocity in the range of 1 hrxe2x88x921 to 15 hr xe2x88x921 with continuous or intermittent injection of alkali solution such as sodium hydroxide of concentration in the range of 0.5-20%, to obtain the desired low mercaptan level petroleum distillates.
In an embodiment of the present invention the alcoholic alkaline solution used is selected from methanolic and ethanolic solution of sodium hydroxide.
In yet another embodiment of the present invention halogenated metal phthalocyanine catalyst used is selected from dichloro cobalt phthalocyanine and dibromo cobalt phthalocyanine.
In yet another embodiment of the present invention the concentration of the catalyst used in the fixed bed is in the range of 0.1 wt % to 1 wt % of activated charcoal.
In yet another embodiment of the present invention the halogenated metal phthalocyanine used is prepared as described and claimed in co-pending U.S. application Ser. No. 09/804,985, filed Mar. 13, 2001.
In yet another embodiment of the present invention the petroleum fraction used is selected from diesel, kerosene and FCC gasoline.
In yet another embodiment of the present invention the temperature is preferably in the range of 20xc2x0 C. to 50xc2x0 C.
In yet another embodiment of the present invention the pressure is preferably in the range of 5 kg/cm2-8 kg/cm2.
In yet another embodiment of the present invention the liquid hourly space velocity (LHSV) is preferably in the range of 1 hrxe2x88x921 to 6 hrxe2x88x921 .
In the sweetening process herein contemplated the undesirable mercaptans contained in a sour petroleum distillate are oxidised to form less deleterious disulphides in the presence of an alkaline reagent with air or oxygen gas. The impregnated support material used is initially saturated with the alkaline reagent, and the alkaline reagent thereafter admixed intermittently or continuously with the sour petroleum distillate passed through the bed. A desired alkalinity of the bed is always maintained during the process. Any suitable alkaline reagent may be employed but aqueous solution of sodium or potassium hydroxide is preferred.
The sweetening process with this catalytic system can be effected at ambient to 100xc2x0 C. temperature, but the preferred temperature range is ambient to 50xc2x0 C. The process may be effected at a pressure from atmospheric to as high as 30 kg/cm2 or more with the preferable pressure range 5-8 kg/cm2. The contact time equivalent to liquid hourly space velocity (LHSV) in the range 1-15, were found to be effective for the oxidation of mercaptans to disulphides. The optimum range for the LHSV was found to be 1-5 for achieving highest conversion. The petroleum distillate and air/oxygen can be passed upwardly or downwardly along with intermittent or continuous alkali injection through the bed. Also, the air may be passed counter current to the petroleum distillate.
The impregnated catalyst bed prepared according to the method of this invention was found to be active and stable. This bed can be used for treating large volume of sour petroleum distillates. As these halogenated metal phthalocyanines are not soluble in aqueous alkaline solution or hydrocarbon, hence they are not leached out from the bed of support material. After prolonged use, the bed gets deactivated and then attempts are made to revive the catalyst activity by regeneration of bed. When even after regeneration activity is not restored, then additional catalyst is reimpregnated by following standard procedure.
The halogenated metal phthalocyanine catalyst impregnated on the support is particularly suitable for the sweetening of wide range of sour petroleum distillates boiling above 140xc2x0 C. like kerosene, jet fuel, fuel oil, naphtha, FCC gasoline and the like in a fixed bed treating system. These higher boiling distillates generally contain mercaptans, which are difficult to oxidize like tertiary mercaptans and aromaticthiols. The catalyst therefore has been evaluated with the feeds doped with various types of mercaptans in different concentrations as given in the examples. Although the supported catalyst of this invention is particularly applicable to the heavier petroleum distillates, it can also be used for the treatment of lower boiling distillates such as natural straight run and the cracked gasolines.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.